The Yugoslav government is leaving its people exposed to poison by suppressing evidence that Nato's bombing has devastated the environment and contaminated the food chain, European environmentalists warn. Tonnes of toxic chemicals are filtering into crops but state agencies have been banned from revealing what areas are at risk because the regime wants to reassure people that the country is returning to normality.

Environmentalists said yesterday that it would take several months to assess the damage, but by then towns near bombed industrial plants could have absorbed hazardous chemicals into their water and food supplies.

The state-controlled media has thrown a cloak of silence over the crisis, leaving a vacuum for scare stories and rumours. Tomato-sellers at Belgrade's Zelena Pijaca market, for instance, advertise their wares as the only ones guaranteed to be radiation-free.

People have been shaken by a statement by Zorka Vukmirovic, a respected professor of organic chemistry, who told Radio Free Europe that if her daughter were pregnant she would advise her to abort.

A preliminary United Nations report has warned of dangers of miscarriages, birth defects and diseases of the nervous system and liver.

A delegation from the European Federation of Green Parties was appalled by a visit to Pancevo, a 150,000-strong town near Belgrade, where fires raged for 10 days after Nato air strikes on its oil refinery, fertiliser and petrochemical plants. The cloud of smoke was more than 10 miles long.

"You could smell the ammonia in the air, it was like sniffing a bottle of bleach," said Niki Kortvelyessy, the delegation's spokeswoman. "No one could tell us how much pollution was there. We were given three sets of figures for the amount of mercury per cubic metre. Mercury is lethal and that ignorance can make a horrendous difference."

The government imposed a 60-day moratorium on publishing environmental information when the war ended on June 9, but Dusan Vasiljevic, president of the opposition Democratic party's ecology committee, doubts that it will be lifted for many months.

"This regime doesn't want to admit the problems, because Serbia is supposed to be victorious," he said. "It is afraid of admitting that the food chain and water supply aren't safe."

Mr Vasiljevic said that government scientists had leaked to him detailed measurements of the damage: more than 1,000 tonnes of ethylene dichloride, 1,000 tonnes of hydrogen chloride (which dissolves to produce hydrochloric acid) and 1,000 tonnes of the corrosive sodium hydroxide had spilled from Pancevo's factories into the Danube.

Fishing downstream from Pancevo is banned but no alert has been issued against drinking tap water or eating produce from polluted towns.

Sonja Prodankovic, an ecologist, said her grandmother, 90, left Pancevo with severe breathing difficulties and close to collapse. "We can't say what damaged her health."

Families near the plants were evacuated on the night of the bombing, but most returned the next day.

Thousands of gallons of ammonia were poured into the Danube to avert a Bhopal-type disaster. The destruction of transformers unleashed highly toxic oil into the water supply of the central Serbia town of Kragujevac.

The water supply of Novi Sad, in the north, was contaminated after 18 tankers were hit and spewed oil.